HDU_1312——二维空间BFS

这题网上都是用DFS做的，我也不知道怎么用BFS做的。。。有个注意点，就是一步也走不动的时候，输出1

Problem Description

There is a rectangular room, covered with square tiles. Each tile is colored either red or black. A man is standing on a black tile. From a tile, he can move to one of four adjacent tiles. But he can't move on red tiles, he can move only on black tiles.

Write a program to count the number of black tiles which he can reach by repeating the moves described above. 

 

 

Input

The input consists of multiple data sets. A data set starts with a line containing two positive integers W and H; W and H are the numbers of tiles in the x- and y- directions, respectively. W and H are not more than 20.

There are H more lines in the data set, each of which includes W characters. Each character represents the color of a tile as follows.

'.' - a black tile 
'#' - a red tile 
'@' - a man on a black tile(appears exactly once in a data set) 

 

 

Output

For each data set, your program should output a line which contains the number of tiles he can reach from the initial tile (including itself). 

 

 

Sample Input

6 9 ....#. .....# ...... ...... ...... ...... ...... #@...# .#..#. 11 9 .#......... .#.#######. .#.#.....#. .#.#.###.#. .#.#..@#.#. .#.#####.#. .#.......#. .#########. ........... 11 6 ..#..#..#.. ..#..#..#.. ..#..#..### ..#..#..#@. ..#..#..#.. ..#..#..#.. 7 7 ..#.#.. ..#.#.. ###.### ...@... ###.### ..#.#.. ..#.#.. 0 0

 

 

Sample Output

45 59 6 13

#include <cstdio>
#include <cstring>
#include <queue>
#define MAX 21
using namespace std;
struct point
{
   int x,y;  
}start;
 
int N,M,dir[4][2]={{1,0},{-1,0},{0,1},{0,-1}};
char map[MAX][MAX];

int Bfs(void);
int main()
{
   while(~scanf("%d %d",&M,&N) && N!=0&&M!=0)
      {
         memset(map,0,sizeof(map));
         for(int i=0;i<N;i++)
            {
               scanf("%s",map[i]);
               for(int j=0;j<M;j++)
                  {
                     if(map[i][j]=='@')
                        start.x=i,start.y=j;   
                  }
            }
         int num=Bfs();
         printf(num==0?"1\n":"%d\n",num);        
      }
   return 0;   
}

int Bfs(void)
{
   int move=0;
   queue<point>p;
   p.push(start);
   point temp,next;
   while(!p.empty())
      {
         temp=p.front();
         p.pop();
         for(int i=0,flag=0;i<4;i++)
            {
               next.x=temp.x+dir[i][0];
               next.y=temp.y+dir[i][1];
               if(next.x>=0&&next.x<N && next.y>=0&&next.y<M && map[next.x][next.y]!='#')
                  {
                     map[next.x][next.y]='#';
                     move++;
                     p.push(next);
                  }
            }
      }
   return move;
}